The present invention relates to continuous phase frequency hopping (CPFH) synchronizing apparatus and methods therefor, and more particularly to CPFH synchronizers having a virtual time base synchronization element and methods therefor.
Systems which make use of frequency hopped signals generally have a problem of epoch synchronization, that is of adjusting the time at which the receiver waveforms are hopped in order to coincide with the hopping of an incoming signal.
A common approach to achieving epoch synchronization in spread spectrum systems involves the use of a means for varying the delay of the spreading modulation. This delay is commonly implemented by either passing the spreading modulation through a variable delay element or by adding or deleting clock cycles in a digital waveform generator. However, by physically changing the time base in this way, an undesirable phase transient is introduced at the moment of correction.
Another approach to providing epoch synchronization involves measuring timing error, closing a first order loop to adjust synchronization by moving the hopping waveform to adjust the time at which hopping occurs to line up with the incoming signal, and then stabilizing the timing by stabilizing the temperature of the receiver. Oven temperature-stabilized timing is however costly and cumbersome.